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I am trying to figure out how the reactivity series comes about. My understanding is that elements with a higher electronegativity will be more reactive than elements with a lower electronegativity, and that elements with a low ionization energy will be more reactive than elements with a high ionization energy.

Here is a chart of electronegativity (from Wikipedia):

This shows electronegativity decreasing (as reactivity increases) down Group 1 and it also decreasing (as reactivity decreases) down Group 7.

Here is a chart of ionization energy:

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This shows ionization energy decreasing (as reactivity increases) down Group 1 and it also decreasing (as reactivity decreases) down Group 7.

Neither electronegativity nor ionization energy can predict both reactivity trends, so what is going on?

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    $\begingroup$ Two thoughts: 1. More reactive with what? 2. The alkali metals are very power reducing agents - their reaction with water gets more explosive as you go down the group (to lower electronegativities). $\endgroup$ – Ben Norris Dec 2 '14 at 11:35
  • $\begingroup$ @BenNorris I guess this question is referring to the metal reactivity series. The WP page says that: "It is used to summarize information about the reactions of metals with acids and water, double displacement reactions and the extraction of metals from their ores." $\endgroup$ – Gaurang Tandon May 16 '18 at 12:27
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With less electronegativity, there is also less ionization energy. This means for metals, it is easier to lose the electrons. When it is easier to lose the electrons, the metal becomes more reactive because it uses less energy to fulfill its goal; to gain a full outer shell.

For nonmetals, the main goal is to gain electrons and not lose them. Thus, an increase in electronegativity and ionization energy means an increase in reactivity because the nonmetals want to hold on to their electrons and gain more vigorously to achieve the full outer shell.

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Reactivity is not only about the tendency of an element becoming an ion( as reflected in ionisation energy and electronegativity). Reactivity takes into account the stability of the produced ion. Often reactions that take place in an aqueous solution takes into account the stability of the ion in water.

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